There are many large metallic structures, such as the hulls of ships, oil storage tanks, gas holders and buildings, which require maintenance. Such maintenance can include cleaning paint, rust and debris from the surface of the structure.
Among the ways these structures are cleaned is grit blasting. Grit blasting is expensive and exposes the operators of the equipment to health hazards.
Another common practice for cleaning large metallic structures is to apply water under high pressure to the surface being cleaned. There are many remotely controlled pressurized water dispensing mobile units in use today for cleaning large metallic surfaces. Generally, these units suffer from one or more shortcomings. Some are very expensive. Others function at much too slow rates. Probably, the most serious shortcoming of such units is that the pressure of the water being dispensed is limited by the "holding" capability of the mobile unit to the surface of the metallic structure being cleaned. As the water pressure is increased, the back pressure tends to separate the mobile unit from the surface being cleaned. Higher pressures are desired because higher pressures increase the effectiveness of the mobile cleaning unit resulting in greater efficiency and reduced costs.